August 2014

August 18, 2014

In today’s new issue of JCB, Cherepanova et al. describe how an oxidoreductase enzyme promotes the glycosylation of newly synthesized proteins in the ER. MagT1, which contains a thioredoxin-like catalytic domain and is mutated in patients with X-linked mental retardation, associates with an oligosaccharyltransferase complex to facilitate access to N-glycosylation sites that would otherwise be obscured by the formation of disulfide bonds during protein folding. More here.

Pichlo et al. reveal how sea urchin sperm detect and respond to single molecules of chemoattractant as they navigate toward the egg. The researchers find that 300,000 copies of the guanylyl cyclase chemoreceptor are densely packed into the sperm flagellum. These chemoreceptors bind to the chemoattractant with extremely high affinity, but the sperm dial down their sensitivity when they experience higher chemoattractant concentrations nearer the egg so that the receptors don’t become saturated. As explained here, the researchers also describe how the receptors are quickly deactivated after binding to the chemoattractant.

Fernandes and Schöck reveal that Lasp, a much shorter version of the giant vertebrate protein nebulin, regulates the architecture of Drosophila muscle sarcomeres. Vertebrate nebulin contains 185 actin-binding repeats and helps to regulate the length of muscle thin filaments. As summarized here, Lasp performs a similar function in flies, despite the fact that it contains just two nebulin repeats, each of which appears to have a slightly different function in the maintenance of sarcomeric structure.

Cai et al. demonstrate how cells restrict the phosphoinositide PtdIns4P to the trans-Golgi network. After determining the crystal structure of the PtdIns4P-binding protein Vps74 bound to the phosphoinositide phosphatase Sac1, the researchers identified mutations that specifically inhibit the interaction between these two proteins and examined their effect on PtdIns4P distribution and Golgi function. As discussed in this week’s In Focus, the results suggest that Vps74 acts as a membrane receptor for Sac1, recruiting the phosphatase to hydrolyze PtdIns4P in early Golgi compartments such as the medial cisternae and thereby maintaining the identity and function of the trans-Golgi network.

And Edens and Levy describe how Protein Kinase C helps to shrink interphase nuclei during Xenopus embryonic development. Senior author Daniel Levy discusses his lab’s findings in this month’s biobytes podcast, where you can also listen to Kara Helmke describe how the microtubule-binding protein TPX2 controls the size of Xenopus meiotic spindles. You can listen below or subscribe in iTunes.

August 04, 2014

There’s a new issue of JCB published today. Let’s take a quick look at some of the papers you can find inside…

Wang et al. describe how stationary-phase yeast cells break down the lipids stored in their lipid droplets. As explained here, the authors propose that yeast deliver lipid droplets to the vacuole via a microautophagy pathway, and then use some of the sterols liberated by the droplets’ degradation to form liquid-ordered domains in the vacuole membrane that facilitate the absorption and digestion of additional lipid droplets.

Hayes et al. reveal that the dramatic shape changes that parasites undergo during their life cycle – or over the course of evolution – might not be as difficult as they appear. Knocking down a single protein called ClpGM6 is sufficient to convert T. brucei trypomastigotes into a state that closely resembles their epimastigote stage. As discussed in this summary, this suggests that parasite shape-shifting may be driven by changes in a few key proteins rather than in wholesale changes in protein expression or in the genome.

Elsewhere, Deakin and Turner demonstrate that the focal adhesion protein paxillin inhibits the microtubule deacetylase HDAC6 to promote microtubule stabilization and cell migration. The pathway also helps relocate the Golgi apparatus toward the front of migrating cells. More here.

And Werner et al. describe how the microtubule-stabilizing protein CLAMP, and the polarity complex formed by Par3, Par6, and atypical PKC promote the radial intercalation of Xenopus epidermal cells. As described in this week’s In Focus, the researchers show that CLAMP and the Par complex stabilize microtubules at the leading edge of cells migrating from the interior of frog embryos so that they can integrate into the outermost layer of the epidermis.

And in this month’s biosights video podcast, Claudia Vasquez and Adam Martin describe how Rho kinase and myosin phosphatase dynamically regulate the pulsatile myosin contractions that promote the stepwise apical constriction of epithelial cells during Drosophila embryogenesis. You can read the paper here and watch the biosights video below. And if you’d like to discuss Vasquez et al.’s findings in your next journal club, you can download everything you could possibly need to give a great presentation by clicking here.

That’s all for today but there are plenty of other interesting papers in today’s new issue that you can discover for yourself by visiting our table of contents page here.

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